At present there exist various types of filter system, generally made up of successive beds of filter elements, such as described, for example, in French patent application FR 2 502 508 filed on Mar. 30, 1981 for "A filter structure, a method of making such structures, and an ultrafiltration device", essentially comprising a porous support of sintered material having relatively large grains, carrying a thinner filter layer of a material that is also sintered but using relatively small grains, . . . . Mention may also be made of European patent application EP 0 634 952 filed under German priority of Apr. 6, 1992 and entitled "A filter element with a permeable and porous undeformable body made of plastics material" . . . .
Naturally, mention can also be made of other filter devices such as those in swimming pool water regeneration circuits which make use essentially of sand: the sand is placed in reservoirs through which the water is caused to flow, but with the drawbacks firstly that sand has high relative density, and secondly that it becomes compacted, thus requiring the water flow direction to be reversed rather frequently since otherwise the porosity of the sand decreases, increasing headloss through the circuit while greatly decreasing its effectiveness.
Also, to make filter cartridges such as those mentioned and described in the above patent applications, special materials are used which are quite expensive to manufacture and implement, but without that giving rise to satisfactory retention efficiency regardless of the elements in suspension in the fluid passing through them, except by decreasing the porosity of said filter. Unfortunately, that also increases the headloss in fluid circulation circuits, thus requiring installations that are large.
The problem posed is thus to be able to make filter systems for physically treating a fluid while using a material which is very cheap to implement, which is inert relative to the fluid it is to filter, and which is capable of retaining a maximum quantity of elements that are in suspension therein, while having porosity through which the fluid passes that is not so small as to increase headlosses excessively, and which is easy to implement, e.g. by being incorporated in any already-existing circuit, or by being used on a site where the filter system must be capable of being buried or located in a closed shelter.